On the Central Highlands battlefield from the night of March 4 to the early morning of March 5, the 25th Regiment controlled Road No. 21, destroyed a convoy of US troops, and took control of the east of Chu Cuc. The second important supply route of the US troops connecting the plains with the Central Highlands was cut off.
On the same day, a unit of the 9th Regiment of the 320A Division took control of Road No.14 at the Ea H'leo section. On the afternoon of March 5, the 2nd Battalion of the regiment ambushed and destroyed 8 of the 15 vehicles in a convoy of the US troops' 45th Regiment from Pleiku to Buon Ma Thuot. On the night of March 5, the 149th Regiment of the 316th Division crossed Road No. 14 to deploy forces in preparation to attack Buon Ma Thuot.
Also on March 5, the main force of the Tri-Thien Military Region, together with Vietnamese local troops and guerrillas from Quang Tri and Thua Thien, opened fire to launch the campaign to liberate Tri Thien.
On the nights of March 5, 6, and 7, more than 3,000 soldiers, including local provincial battalions, two special forces battalions, more than a hundred armed task forces and local armed forces, along with political forces and command agencies at all levels, secretly and safely passed through the enemy's defence system, bases, posts, and dense network of informants to infiltrate the plains and important areas.
Meanwhile, at the Dong Xoai base on March 5, in implementing the plan to coordinate the entire southern battlefield, Le Duc Anh, Deputy Commander of the Region, directly assigned the task to the 7th Division (the 4th Corps) and armed forces of 6th and 7th Military Regions to open a new front in the northeast of Saigon, capture Dinh Quan, liberate Road 20 and Lam Dong Province.
